GB-A-2,020,734 discloses a prior-art door opener, the purpose of which is to provide both motor-driven and manual operation of, for example, door leafs. A motor-driven opening or closing may, for instance, be initiated by someone passing a detection sensor, or by the person who desires to open the door pressing a button which activates the drive motor of the opener. For safety reasons, it is important that the door leaf can be opened manually. For example, if a power failure should occur, it must be possible to open the door leaf manually. Door openers of this type are often used in doors in public buildings such as hospitals, libraries, banks and shops. Such door openers are also used when tailoring buildings to the needs of disabled people.
One disadvantage associated with a door opener of this kind is that it has many components. It is, therefore, both complex and expensive to manufacture as well as bulky, which makes the installation difficult. The door opener is mounted either directly on the door leaf or on the wall above the door leaf. If the space between the upper edge of the door leaf and the ceiling is small, the door opener has to be mounted in a recess in the ceiling, which is a lengthy and expensive procedure. Moreover, in operation the complex structure causes an annoying sound level.
Although door openers of this kind allow manual conveniencing especially elderly and disabled people.
Furthermore, if the door is opened manually in a violent manner, either intentionally or by vandalizing kicks and violent blows, the door opener drive motor risks being damaged.
Further examples of prior art are the devices disclosed in DE-A 3 730 114, EP-A-169 296, EP-A-632 181, U.S. Pat. No. 2,371,336, U.S. Pat. No. 2,075,000, U.S. Pat. No. 3,886,425 and U.S. Pat. No. 3,653,154, which, however, also suffer from drawbacks described above.